1. Field of the Invention
The present invention relates to articles comprising a substrate bearing a coating formed of blends of polymers.
2. Discussion of the Prior Art
The utilitarian aspects of many articles which have the desired properties of durability, strength, optical clarity, etc. can be adversely affected by the surfaces of those articles. As one example, lenses made of glass or polycarbonates have surfaces that, upon encountering moist air, can fog up, impairing the transparency of the lenses. U.S. Pat. Nos. 4,369,229 and 4,462,665 describe the use of optically clear polymer blends comprising vinyl lactam polymers and water-insoluble copolymers of a hydrophobic, water-insoluble ethylenically unsaturated monomer, an ethylenically unsaturated monomer containing an acid group, and optionally a hydrophilic ethylenically unsaturated monomer free from acidic groups as coating materials for water insensitive substrates. The hydrophobic polymer requires a monomeric component containing an acidic group. Acidic groups are known to catalyze many chemical reactions, some of which could limit the usefulness of the coated product. Coatings derived from the blends of this invention have a potential pH sensitivity, particularly under highly alkaline conditions, because of the presence of the acidic functional groups. In the area of medical applications, acid groups could cause protein deposition, which may be undesirable for biocompatibility. Moreover, the polymeric blend requires components that are not readily available.
As another example, polyester film, a preferred backing for tapes and magnetic media, exhibits poor adhesion to most other polymers, thus making it difficult to take advantage of the desirable physical properties of polyester. Several techniques, including corona discharge, electron bombardment, treatment with phenolics, or priming with copolymers of vinylidene chloride, have been used to modify polyester films to improve adhesion. However, many of these techniques require expensive equipment and frequently are of limited versatility.
It would be desirable to develop a coating material that has wide utility, e.g. for providing hydrophilicity to hydrophobic surfaces, for priming surfaces to promote adhesion.